The invention concerns a fuel tank and more particularly a fuel tank for a motor vehicle.
A typical form of fuel tank for a motor vehicle comprises a filling opening for introducing fuel into the tank in a refuelling procedure, at least one fuel delivery pump to feed fuel from the fuel tank to the engine of the motor vehicle, and at least one operational vent means and at least one refuelling vent means.
It will be noted in that respect at this point that the term operational vent means is used herein to denote a vent means for venting the fuel tank during operation of the vehicle, for venting fuel vapor for example from the tank due to fluctuations in temperature or caused by swirl or surge movements of the fuel in the fuel tank in response to dynamic movement of the motor vehicle in which the fuel is disposed. The term refuelling vent means is used herein to denote a vent means operative to vent the tank upon a tank filling or refuelling procedure.
The vent means are connected to a fuel vapor filter by way of at least one vent line while connected upstream of the fuel vapor filter is at least one bead removal container for removing liquid beads or droplets of fuel from the fuel vapors carried in the vent line.
It will be appreciated that fuel tanks of the above-indicated general configuration which nowadays are usually formed in one or more pieces from plastic material are systems which are optimised in terms of hydrocarbon emissions. As is known, certain plastic materials, for example polyethylene, are permeable in relation to hydrocarbons. For that reason, fuel tanks of plastic material are often of a multi-wall configuration or are made from multi-layer extrudates with incorporated barrier layers for hydrocarbons to prevent diffusion thereof through the wall of the tank to the surrounding atmosphere. It is in the meantime possible for fuel tanks of plastic material for hydrocarbon fuels to be designed in such a way as to be very substantially diffusion-resistant in relation to such fuels. Possible sources of hydrocarbons emissions however are still connecting nipples, valves, hoses, fitting openings and the like on or in the tank wall. It will be appreciated that lines and conduits going to and from the fuel tank also constitute possible sources of fuel emission. It is therefore desirable for as few connections and like components to be provided on a fuel tank and for as many other units of equipment which are required to ensure a supply of fuel to an internal combustion engine of a motor vehicle to be disposed in the interior of the fuel tank.
It will further be appreciated that manufacturing and assembly costs for fuel tanks and fuel feed systems which are optimised in terms of fuel emissions are to be kept within reasonable limits, either in the case of fuel tanks of plastic material which are made in one or more parts or in the case of fuel tanks of metal which are similarly made up of a plurality of parts.
In the case of multi-part fuel tanks comprising two or more casing portions, arranging a large part of the lines and other units of equipment for providing for the supply of fuel to the motor vehicle engine in the interior of the fuel tank and fixing them therein will involve a comparatively low level of assembly expenditure. That however is a more difficult proposition in the case of one-piece plastic fuel tanks which are formed by extrusion blow molding. In the case of such a fuel tank the body of the tank has to be blow-molded in part around the installation units in the procedure for producing the tank or the installation units have to be subsequently fitted into the tank through fitting openings which are to be subsequently gas-tightly closed.
Although the installation units of the fuel tank and the fuel supply system which is to be provided thereon are to be designed to last the service life of the fuel tank, it is nonetheless often desirable to reduce the number of components used and to make some components such as for example the fuel pump or a suitable fuel delivery unit interchangeable for repair or maintenance purposes.
An object of the present invention is to provide a fuel tank for a motor vehicle, which is improved in terms of its emission values, while further being simplified in respect of its structure.
Another object of the invention is to provide a motor vehicle fuel tank which involves a reduction in connecting locations and like units which are liable to constitute a source of emission from the tank.
Still another object of the present invention is to provide a fuel tank so designed that a significant proportion of connections thereon are moved into the tank so as to make a considerable contribution to reducing possible hydrocarbon emissions therefrom.
Still a further object of the present invention is to provide a motor vehicle fuel tank which affords enhanced ease of replaceability of fuel tank components which are liable to require repair and/or maintenance.
In accordance with the principles of the present invention the foregoing and other objects are attained by a fuel tank for a motor vehicle, comprising at least one filling opening, at least one fuel delivery pump, at least one operational vent means and at least one refuelling vent means. The vent means are connected by way of at least one vent line to a fuel vapor filter. Connected upstream of the fuel vapor filter is at least one bead removal container. At least the bead removal container and the refuelling vent means are combined to form a functional unit in the form of a vent unit.
As will be seen in greater detail from an embodiment of a fuel tank in accordance with the present invention as described hereinafter combining a plurality of components of the vent system of the fuel tank to constitute a unit can simplify assembly of the tank and minimise the number of connections of the entire vent system. If the fuel tank is made from plastic material, which is the preferred option here, the vent unit provided in accordance with the invention can contribute to reducing the number of connecting locations and weld locations involved in the vent system. A further advantage of this arrangement is that this involves a significant number of the connecting locations involved in the assembly being moved into the tank, which makes a quite considerable contribution to reducing hydrocarbon emissions.
In a preferred feature of the invention the vent unit is arranged overall releasably and interchangeably in the fuel tank. In that way, if the vent unit has for example a defective valve, it can be quite readily replaced or repaired. In a further preferred feature the vent unit can be in the form of an insert which is adapted to close a fitting opening in the wall of the fuel tank.
The vent unit can be for example in the form of a cover closure which is sealed with a cover flange in relation to the tank wall. The cover flange can then be welded to the tank wall. Alternatively, it can be provided that the cover flange is braced in relation to the tank wall by means of a union nut, with the interposition of one or more seals. In that case, a suitable screwthreaded connecting portion or an additional screwthreaded ring is to be provided in or on the tank wall.
It will be appreciated that both the fuel feed afforded by the fuel delivery system to the motor vehicle engine and possibly the return therefrom can be taken through the above-mentioned cover closure of the vent unit. It may also accommodate cable ducting means for the fuel delivery pump, a sender such as a fuel level sensor and the like. This affords the advantage that it is possible to save on an additional cover closure and an additional fitting opening for the fuel delivery unit, whereby the number of openings in a diffusion-tight tank wall can also be reduced. In that case the fuel delivery unit can be fitted into the fuel tank through the fitting opening for the vent unit.
In a further preferred feature of the invention the cover closure is in the form of a carrier means for the vent unit.
In a further preferred feature of the invention the fuel tank includes at least one roll-over valve in the vent unit, more preferably disposed in the immediate proximity of the cover closure. In the installation position of the tank, the roll-over valve would be arranged approximately in the upper third of the bead removal container adjoining the cover closure.
In still another preferred feature of the invention at least one safety pressure relief valve can be disposed in the vent unit, operable to permit emergency venting of the fuel tank when the operational vent means and the refuelling vent means are closed. Such a safety valve for example prevents an excessively increased pressure from building up in the fuel tank in the case of the tank being overfilled. It is therefore appropriate for the safety valve to be provided on the vent unit in such a way that the safety valve is disposed in the gas phase in the fuel tank, when the vehicle is in any reasonably possible inclined position.
Preferably, there are a plurality of operational vent means which are connected to the vent unit by way of a common vent conduit or a plurality of vent conduits. The vent unit thus also serves to bring together all the vent ducts from the fuel tank.
The operational vent means can be in the form of operational vent valves with or without a pressure-holding function or alternatively in the form of simple vent nipples.
Desirably, the refuelling vent means is in the form of a refuelling vent valve, but it is also possible to provide a shut-off valve in the filler pipe of the fuel tank, to actuate a shut-off mechanism of a refuelling gun in order thereby to terminate a refuelling procedure, so that the refuelling vent means does not have to involve any shut-off function or any pressure holding function.
A preferred configuration in accordance with this invention however provides that the operational vent means and also the refuelling vent means are in the form of valves. In that case the operational vent means will be such as to close due to actuation by a float when fuel is present thereat. A pressure holding function for the operational vent valve is ensured by a pressure relief valve disposed on the downstream side thereof.
The bead removal container is desirably provided with a labyrinth configuration or with internally disposed baffle walls so that liquid hydrocarbons contained in dispersed form in the fuel vapors can condense out in the bead removal container. The bead removal container is to be provided for the reason that in dynamic operation of the motor vehicle in which the fuel tank of the invention is fitted or when refuelling the motor vehicle, it is not impossible for a mixture of liquid and gaseous fuel to be entrained by way of the vent conduits. It is appropriate to avoid as far as possible liquid hydrocarbons being passed to the fuel vapor filter as that can adversely affect the regeneratability thereof. In general such a fuel vapor filter is in the form of an activated carbon filter which is regenerated by way of the combustion air feed to the engine.
In accordance with the invention it is preferably provided that the refuelling vent valve is arranged immediately beneath the bead removal container or on same at the upstream side thereof. The valve casing surrounding the refuelling vent valve, like the bead removal container, can be provided with labyrinth fitments therein.
As in accordance with the invention the bead removal container can be arranged in the fuel tank, it is not impossible that, when there is a high level of fuel in the tank, there is no or only a slight difference in level between the level of liquid in the bead removal container and the level of fuel in the fuel container. In that case, it is preferable to provide means for actively emptying the bead removal container into the fuel tank against a fall in level or when there is a slight difference in level between the level of fuel in the fuel tank and the level of liquid in the bead removal container. In that case the operational vent means can be in the form of one or more nipples, in which respect it is possible to accept that a certain amount of liquid hydrocarbons passes into the bead removal container by way of the vent means. The volume of the bead removal container can be such that the entrainment of liquid hydrocarbons through the vent conduits into the bead removal container can be tolerated within certain limits.
For the purposes of actively emptying the bead removal container into the fuel tank, it is possible for example to connect a drain conduit thereof to the suction intake side of a pump, for example a suction jet pump. The suction jet pump can be operated in the manner known in relation to such devices, by way of a flow portion of fuel which is branched off the flow of fuel being conveyed to the engine. Alternatively, it is possible for example in the case of a fuel delivery system with a return from the engine, for the suction jet pump to be operated by way of the return flow from the engine. It is preferable to provide an additional suction jet pump for the purposes of actively emptying the bead removal container. Depending on the respective configuration of the fuel tank which can be of a complex structure involving a plurality of filling levels therein, for example in different compartments of the tank, suction jet pumps are often to be provided in any case for emptying various compartments in the tank into the reservoir or swirl pot of a fuel delivery unit of the tank.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of a preferred embodiment of the invention.